There is currently a growing demand for power devices which offer improved operating efficiency and higher speed. Power MOSFETs have inherently higher switching speeds than bipolar transistors and thus are strong candidates for use in high frequency switch mode power supplies and inverters. The fabrication of MOSFETs include many diffusion and wet etch steps to form the various electrodes of the device in a substrate of silicon or the like, which materials are readily susceptible to such process steps.
However, silicon and the like have a relatively low breakdown voltage and poor thermal conductivity, resulting in devices which are rather severely limited in voltage, power, and operating temperature characteristics.
Some attempts have been made to rectify these shortcomings by fabricating lateral MOSFETs from silicon carbide, which is capable of withstanding a much larger breakdown voltage, has a better thermal conductivity, and a larger bandgap which permits operation at higher temperatures. However, lateral MOSFETs have the disadvantage of requiring much larger die area for devices capable of performing at an equivalent level with vertical structures.
It is a purpose of the present invention to provide a relatively easy method of fabricating vertical MOSFETs from silicon carbide.
It is a further purpose of the present invention to provide a method of fabricating vertical MOSFETs from silicon carbide without requiring difficult diffusion and/or implant steps.
It is a further purpose of the present invention to provide a method of fabricating vertical MOSFETs from silicon carbide without requiring difficult wet etch steps.